1. Field of the Invention
The invention relates to a vehicular braking control apparatus and, more particularly, to a vehicular braking control apparatus having a function of detecting an abnormality of a stroke simulator among vehicular braking control apparatuses that electronically control the braking force applied to wheels of a vehicle. The invention also relates to an abnormality detection method for a vehicular braking apparatus and, more particularly, to a method for detecting an abnormality of a stroke simulator.
2. Description of the Related Art
A known braking control apparatus of a vehicle is a control apparatus (electronically controlled brake) that electrically controls the hydraulic pressure supplied to a wheel cylinder for actuating a braking apparatus. Such a control apparatus, if an abnormality occurs in the control system, stops the electrical control, and supplies hydraulic pressure from a master cylinder that generates a hydraulic pressure corresponding to the amount of brake operation, thereby starting a manual control. Therefore, technologies for reliable determination regarding abnormality of the control system and the braking apparatus have been developed (e.g., Japanese Patent Application Laid-Open Publication No. 10-100884 (paragraphs [0078] to [0093], and FIG. 6), and Japanese Patent Application Laid-Open Publication No. 11-59389 (paragraphs [0081] to [0099], and FIG. 3).
The technology disclosed in Japanese Patent Application Laid-Open Publication No.10-100884 detects the state of operation of hydraulic pressure sensors used for the aforementioned determination, and determines whether there is a sensor abnormality by temporarily allowing conduction through the hydraulic pressure passageway where each sensor is disposed and then comparing the outputs of the hydraulic pressure sensors.
The technology disclosed in Japanese Patent Application Laid-Open Publication No. 11-59389 locates a fault on the basis of the wheel cylinder pressures that occur during the pressurization via the master cylinder and during the electrically controlled pressurization.
During the electronic control in such an electronically controlled brake, the hydraulic fluid of the wheel cylinder and the hydraulic fluid of the master cylinder are disconnected from each other, and therefore, the resistance to the operation of the brake pedal performed by a driver is insufficient if no particular device is provided. To cause the brake pedal to produce a reaction force corresponding to the amount of pedal operation, a stroke simulator is disposed. If this stroke simulator portion has an abnormality, such as liquid leakage or the like, while the electronically controlled braking system (including the braking control system) does not have an abnormality, there is no problem in the braking control. However, if pressurization via the master cylinder is attempted in the event of abnormality of the electronically controlled braking system, there is a possibility of a reduction in the pressurization provided that the stroke simulator has an abnormality. Therefore, it is necessary to detect whether the stroke simulator has an abnormality. However, since the stroke simulator is disposed outside the electronically controlled braking system, an effective technique for the abnormality detection has not been found.